Pioneer SA-9900 Repair Question

abwman

New Member
The amp seems to be working fine, but then if I increase volume, the output will cut off and on (with a clicking noise that would seem to indicate an internal protective relay has been triggered) until I reduce volume enough to prevent that from happening. I'm not bringing the volume up to any very high levels, certainly not anything that should cause a problem. Any thoughts on what the problem is and what steps I should take to cure or repair would be appreciated.
 
The first thing to do is to determine exactly what the clicking
is. Is it indeed the protection relay or somthing else making noise.
I would want to seperate the pre and main amp. Then drive the
power amp with a different signal source just to see which side
really deserves your attention before going too far.
 
Like Glen65 said, divide and conquer. Make sure the amp section is really the troublemaker. Its also possible that the protection circuits are farking things up. Do an AK search on troubleshooting Pioneer amps and receivers. I'm sure you'll find some good advice from the people who know which end of the soldering iron to hold.

Is this a unit you found at a Goodwill or is this a treasured heirloom that suddenly started acting funky? Put another way, did this problem just appear out of the blue?

Get the schematics. When you're poking around inside an amp, you need to know what shouldn't be poked (or prodded). Besides, when you've got it running again you can tune the bias & offset (you *were* going to do that - right?). AG Tannenbaum and ebay are good sources for schems.

Pop the top of the amp and look around for the obvious stuff. Overheated components that might be near electrolytic caps. You can tell when they have vented. Shrunken plastic covers and popped tops.

Then there's the Audiokarma equivalent of the LaBrea tar pits.
Some call it Sansui snot while others refer to it as Yamaha barf.
Its the *dreaded* circuit board glue. It ages and through the wonders of modern chemistry, becomes conductive and sometimes even acidic (!). Carefully remove it with an Xacto knife. You might have to desolder the afflicted parts from the board to get all the gunk off.

That ought to keep you busy until EW gets online.
 
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Sometimes sheer stupidity is the answer

Thanks for the responses. Fortunately I didn't have to mess with the innards because the answer was totally on me. Speaker connections were screwy so that the amp thought it was dealing with less than 4 ohm speakers! Once that possibility was pointed out to me (through another web site) I checked and sure enough, that was the culprit. Now I know you can't connect multiple amps to the same speakers, even if you only use one at a time. I'm probably lucky I didn't mess things up worse. I'm posting this so that some other dumb _____ may see it someday and learn from my mistake.

By the way, this is not a thrift store get, but an amp I've had since I purchased it many years ago, but recently took off the shelf again.

Now I need to see if I can handle to DC offset stuff. I'm sure I can do the measuring, but if there are issues, I don't trust myself to handle the adjustments.
 
abwman said:
Thanks for the responses. Fortunately I didn't have to mess with the innards because the answer was totally on me. Speaker connections were screwy so that the amp thought it was dealing with less than 4 ohm speakers! Once that possibility was pointed out to me (through another web site) I checked and sure enough, that was the culprit. Now I know you can't connect multiple amps to the same speakers, even if you only use one at a time. I'm probably lucky I didn't mess things up worse. I'm posting this so that some other dumb _____ may see it someday and learn from my mistake.

By the way, this is not a thrift store get, but an amp I've had since I purchased it many years ago, but recently took off the shelf again.

Now I need to see if I can handle to DC offset stuff. I'm sure I can do the measuring, but if there are issues, I don't trust myself to handle the adjustments.

Good to see that you sorted out the most pressing problem. You should nonetheless measure the DC offset. If it is OK, you don't have to mess with the innards. If it is not OK, AK is the place to ask for advice.

Take care!

- Harald
 
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